BRAHMAPUTRA FLOODING AND TREE RINGS

Subject: Environment

Context: Destructive flooding of the Brahmaputra will probably be more frequent than previously estimated, even without factoring in the effects of human-driven climate change, says a new study which assembled a chronology of the river’s flow for the last seven centuries.

Concept:

• In the current study, based on the tree rings data, they said the earlier estimates likely fall short by about 40 per cent.
• The scientists also looked at data from the rings of ancient trees sampled at 28 sites in Tibet, Myanmar, Nepal and Bhutan — at sites within the Brahmaputra watershed.
• Since the rings grow wider when the soil moisture is high, the researchers could indirectly piece together rainfall and resulting river runoff during these years.
• Based on the analysis, they assembled a 696-year chronology, running from 1309 to 2004, and found that the widest rings lined up neatly with known major flood years.
• According to the scientists, anyone using the modern discharge record to estimate future flood hazard would be underestimating the danger by 24 to 38 per cent, based solely on natural variations.
• They cautioned that human-driven warming would have to be added on top of these estimates.